The present invention relates to an electrical installation device, for example a low voltage switch, which is configured for fastening in an attachment position on a carrier rail, the device including a sliding latch that is shaped in one piece to an instrument housing wall made of an insulating plastic, and wherein the sliding latch is
(a) movable in a locking direction outside of the housing bottom transversely to an attachment direction and to the carrier rail direction;
(b) pivotally connected with a housing wall by way of a flexible web that is spring elastic in the locking direction;
(c) equipped with a detent lug which, in the locking direction, grips behind the carrier rail; and
(d) returnable against the spring elasticity of the flexible web from its locked position into a release position by way of an actuating end facing away from the detent lug.
The known installation device is thus fastened to the carrier rail by means of its instrument housing. For this purpose the instrument housing is usually provided with two fastening elements. One fastening element is essentially rigidly shaped to an instrument housing wall and, when the housing bottom is placed onto the carrier rail, clamps one longitudinal edge of the rail between itself and the housing bottom. The second longitudinal rail edge which extends parallel to the first longitudinal rail edge, once the installation device is attached, is clamped in between the housing bottom and a movable sliding latch. The sliding latch is then in its locked position. It is movable in a locking direction between its locked position and its release position. Due to the mobility of the sliding latch, the instrument housing is fastened to a carrier rail, during the attachment process, in the manner of a snap fastening. To release the fastening, the sliding latch is pushed into its release position.
Such an installation device is disclosed, for example, in German Patent No. 3,728,907.A1. The sliding latch disclosed there is shaped in one piece and movably connected to the instrument housing by means of a flexible web that extends perpendicularly to the plane of the carrier rail. At its end facing away from the detent lug that serves to fix it to the longitudinal edge of the rail, the flexible web is extended in the locking direction by way of an actuation end. An actuation tool, for example, a screwdriver blade, engages in the actuation end to move the sliding latch from its locked position into its release position. The movement of the actuating end is here guided by a slotted guide that is shaped in one piece to the shell body and in which the actuation end rests.
A drawback of the prior art installation device is the arrangement and configuration of the sliding latch. The sliding latch constitutes an extension of the moving end of the flexible web. In order for the sliding latch to produce a mechanically stable fixation of the instrument housing on the carrier rail, the flexible web must be made relatively rigid in spite of the elasticity required of it so that the sliding latch remains reliably in its locked position and is able to exert a sufficiently strong pressure force on the carrier rail. The mechanically stable and relatively rigid configuration of the flexible web, however, requires greater exertion of force by the user to move the sliding latch from its locked position into its release position, while a more elastic configuration of the flexible web results in reduced pressure forces on the part of the sliding latch acting on the carrier rail. A stable attachment of the instrument housing on the carrier rail is therefore not ensured. This safety risk is additionally augmented in that the sliding latch, due to natural wear of the flexible web during the bending processes, is removed farther and farther from its original locked position and, in the course of the service life of the flexible web, the sliding latch, as a component that is carried only by the flexible web itself, permanently exerts lower pressure forces on the carrier rail.